Hybridomas have been prepared with A/J spleen which secrete monoclonal antibodies with specificity for the phenylarsonate (Ar) hapten and which carry idiotypes that are cross-reactive within the strain. Some are related but not identical to the major idiotype. The antibodies will be studied serologically to determine the nature of the variations that exist. We will continue collaborative studies on a T cell factor which suppresses delayed-type hypersensitivity to the Ar hapten in the A strain and which carries the major idiotype. By genetic and serological studies we hope to obtain evidence as to whether a light chain component is present. We will attempt to prepare a T cell hybridoma that synthesizes the factor; if successful, sequencing of internally radiolabeled factor may be feasible. Studies of the mechanism of induction of idiotype-specific suppressor T cells will be continued with emphasis on possible interactions among suppressor T cells that carry idiotypic or antiidiotypic receptors. Other investigations will be concerned with the extent to which immune responses are dominated by secondary B cells after initial priming; the repertoires of L chains in various strains of mice, as reflected by their capacity to supply an idiotypically defined L chain; and an attempt to identify antigens to which antibodies in the cerebrospinal fluid of patients with multiple sclerosis are directed.